FEATURES OF THE DEVELOPMENT OF A CIRCULAR SOLAR FLARE

Анотація

We present the results of the analysis of
morphology and evolution of the circular solar flare using
H-alpha images. H-alpha filtergrams were obtained with
the Meudon spectroheliograph. The active region NOAA
9087 had a complex multipolar magnetic field configura-
tion. New magnetic fluxes emerged during the evolution of
this flare-productive active region. The high flare and surge
activity was observed in the active region.
According to Solar Geophysical Data (SGD) the
3N/M6.4 class solar flare occurred on July 19, 2000 at
06:37 UT, peaked at 07:23 UT and lasted 2.5 hours. Two
bright kernels appeared near large positive-polarity sunspot
at the beginning of the flare. In a few minutes bright kernels
occurred in the center of the active region near polarity in-
version line. Space solar observatory Yohkoh detected a
hard X-ray (HXR) coronal source in the 13.9-22.7 keV and
22.7-32.7 keV energy bands in this location.
New kernels appeared in the southern and eastern parts
of the active region at the boundaries of the chromospheric
network. They brightened sequentially clockwise, which
may indicate a slipping reconnection. Magnetic reconnec-
tion was observed in the main phase of the flare in the east-
ern part of the active region. In the late flare phase arcade
of post-reconnection EUV loops connected the main flare
ribbon with the place of repeated reconnection. Additional
heating may be required for the explanation of the long
flare decay phase.
Flare ribbons of the circular shape were formed. The
complex magnetic configuration of the studied active re-
gion and circular shape of the ribbons suggest that it had a
fan-spine magnetic topology with null points. Possibly,
flare ribbons are the locations of intersections of the fan
quasi-separatrix layer with the chromosphere. They ap-
peared as a result of heating or particle beam moving along
a quasi-separatrix layer from a source in the corona.